Some states do a visual check (usually with a mirror) for elimination of emission equipment, including pre cats. The pre-cats function primarily as the main source of emission cleanup, where the downstream cat is a secondary cleanup source, since the precats are monitored. Technically you can remove the secondary cat and still pass emissions on this vintage of car. I had a customer with an 03 Elantra with a gutted secondary cat and it passed the smog check due to the precat doing the work. Emissions was a bit higher, but within allowable limits of the state/federal government standards. On some cars, particularly newer cars, the precat and secondary cat are monitored with separate o2 sensors. My 09 Mazda 3, which was CA compliant as required by WA state had 3 separate o2 sensors, one in the manifold, one behind the precat and one after the secondary cat.